Temperature-based breakthrough detection and pressure swing adsorption systems and fuel processing systems including the same

ABSTRACT

Pressure swing adsorption (PSA) assemblies with temperature-based breakthrough detection systems, as well as to hydrogen-generation assemblies and/or fuel cell systems containing the same, and to methods of operating the same. The detection systems are adapted to detect a measured temperature associated with adsorbent in an adsorbent bed of a PSA assembly and to control the operation of at least the PSA assembly responsive at least in part thereto, such as responsive to the relationship between the measured temperature and at least one reference temperature. The reference temperature may include a stored value, a previously measured temperature and/or a temperature measured elsewhere in the PSA assembly. In some embodiments, the reference temperature is associated with adsorbent downstream from the adsorbent from which the measured temperature is detected. In some embodiments, the PSA cycle and/or components thereof are determined at least in part by the relationship between the measured and reference temperatures.

RELATED APPLICATION

This application is a continuation-in-part of, and claims priority to,U.S. patent application Ser. No. 11/055,843, which was filed on Feb. 10,2005, now U.S. Pat. No. 7,393,382, and which claims priority to U.S.Provisional Patent Application Ser. No. 60/638,086, which was filed onDec. 20, 2004. This application also claims priority to U.S. ProvisionalPatent Application Ser. No. 61/026,613, which was filed on Feb. 6, 2008.The complete disclosures of the above-identified patent applications arehereby incorporated by reference for all purposes.

FIELD OF THE DISCLOSURE

The present disclosure is directed generally to pressure swingadsorption systems and hydrogen-generation and/or cell systemsincorporating the same, and more particularly to such systems thatutilize a temperature-based breakthrough detection system.

BACKGROUND OF THE DISCLOSURE

A hydrogen-generation assembly is an assembly that converts one or morefeedstocks into a product stream containing hydrogen gas as a majoritycomponent. The produced hydrogen gas may be used in a variety ofapplications. One such application is energy production, such as inelectrochemical fuel cells. An electrochemical fuel cell is a devicethat converts a fuel and an oxidant to electricity, a reaction product,and heat. For example, fuel cells may convert hydrogen and oxygen gasesinto water and electricity. In such fuel cells, the hydrogen gas is thefuel, the oxygen gas is the oxidant, and the water is the reactionproduct. Fuel cells typically require high purity hydrogen gas toprevent the fuel cells from being damaged during use. The product streamfrom a hydrogen-generation assembly may contain impurities, illustrativeexamples of which include one or more of carbon monoxide, carbondioxide, methane, unreacted feedstock, and water. Therefore, there is aneed in many conventional fuel cell systems to include suitablestructure for removing impurities from the product hydrogen stream.

A pressure swing adsorption (PSA) process is an example of a mechanismthat may be used to remove impurities from an impure hydrogen gas streamby selective adsorption of one or more of the impurities present in theimpure hydrogen stream. The adsorbed impurities can be subsequentlydesorbed and removed from the PSA assembly. PSA is a pressure-drivenseparation process that utilizes a plurality of adsorbent beds. The bedsare cycled through a series of steps, such as pressurization, separation(adsorption), depressurization (desorption), and purge steps toselectively remove impurities from the hydrogen gas and then desorb theimpurities. A concern when using a PSA assembly is preventingbreakthrough, which refers to when the adsorbent in a bed has beensufficiently saturated in adsorbed impurities that the impurities passthrough the bed and thereby remain with the hydrogen gas instead ofbeing retained in the bed. Conventionally, breakthrough preventionrequires either intentional underperformance of the PSA assembly or theuse of expensive composition-based detectors, such as carbon monoxidedetectors, to determine when even a few parts per million (ppm) ofcarbon monoxide have passed through a bed. By “intentionalunderperformance,” it is meant that the PSA assembly is operatedinefficiently, with each bed being used for impurity adsorption for onlya subset of its capacity to provide a potentially wide margin of unusedadsorbent and thereby hopefully prevent breakthrough. An advantage ofsuch a process is that the cost and equipment required is reduced;however, the lack of actual breakthrough detection and the inefficientoperation of the system may outweigh the cost and equipment savings,especially when it is realized that the composition of the stream to bepurified may fluctuate due to malfunctions or other causes elsewhere inthe hydrogen-generation assembly.

SUMMARY OF THE DISCLOSURE

The present disclosure is directed to PSA assemblies withtemperature-based breakthrough detection systems, as well as tohydrogen-generation assemblies and/or fuel cell systems containing thesame, and to methods of operating the same. The PSA assemblies includeat least one adsorbent bed, and typically a plurality of adsorbent beds,that include an adsorbent region including adsorbent adapted to removeimpurities from a mixed gas stream containing hydrogen gas as a majoritycomponent and other gases. The mixed gas stream may be produced by ahydrogen-producing region of a fuel processing system, and the PSAassembly may produce a product hydrogen stream that is consumed by afuel cell stack to provide a fuel cell system that produces electricalpower. The PSA assembly includes a temperature-based breakthroughdetection system that is adapted to monitor at least one temperatureassociated with the adsorbent in each bed and responsive at least inpart to the measured temperature to control the operation of at leastthe PSA assembly, and optionally other components of thehydrogen-generation assembly and/or fuel cell system utilized therewith.In some embodiments, the breakthrough detection system may beimplemented to control the operation of at least the PSA assembly toprevent actual breakthrough from occurring. In some embodiments, thebreakthrough detection system may be implemented to set, regulate,calculate, or otherwise determine at least a duration or other aspect ofa step of the PSA cycle or the entire PSA cycle. Responsive at least inpart to the measured temperature, the system may be adapted, in someembodiments, to shut down the PSA assembly and/or generate at least onealert or other notification. In some embodiments, the detection systemis adapted to initially determine and/or vary at least the time of oneor more steps, such as the adsorption step, utilized by the PSAassembly, if not the total PSA cycle time. In some embodiments, thedetection system is adapted to transition between steps of a PSA cycle.In some embodiments, the detection system is adapted to regulate, suchas increase, reduce, or otherwise vary the total PSA cycle time and/orcomponent steps thereof responsive at least in part to the measuredtemperature and/or the detection of a breakthrough condition. In someembodiments, the measured temperature is compared to a referencetemperature. In some embodiments, the reference temperature is anothermeasured temperature of the adsorbent or other portion of the PSAassembly. In some embodiments, the reference temperature is a previouslymeasured or selected temperature, including a stored temperature orthreshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an illustrative example of anenergy-producing and consuming assembly that includes ahydrogen-generation assembly with an associated feedstock deliverysystem and a fuel processing system, as well as a fuel cell stack, andan energy-consuming device.

FIG. 2 is a schematic view of a hydrogen-producing assembly in the formof a steam reformer adapted to produce a reformate stream containinghydrogen gas and other gases from water and at least onecarbon-containing feedstock.

FIG. 3 is a schematic view of a fuel cell, such as may form part of afuel cell stack used with a hydrogen-generation assembly according tothe present disclosure.

FIG. 4 is a schematic view of a pressure swing adsorption assemblyincluding a temperature-based breakthrough detection system according tothe present disclosure.

FIG. 5 is a schematic cross-sectional view of an adsorbent bed that maybe used with PSA assemblies according to the present disclosure.

FIG. 6 is a schematic cross-sectional view of another adsorbent bed thatmay be used with PSA assemblies according to the present disclosure.

FIG. 7 is a schematic cross-sectional view of another adsorbent bed thatmay be used with PSA assemblies according to the present disclosure.

FIG. 8 is a schematic cross-sectional view of the adsorbent bed of FIG.6 with a mass transfer zone being schematically indicated.

FIG. 9 is a schematic cross-sectional view of the adsorbent bed of FIG.8 with the mass transfer zone moved along the adsorbent region of thebed toward a distal, or product, end of the adsorbent region.

FIG. 10 is a schematic cross-sectional view of a portion of a PSAassembly that includes at least one adsorbent bed and atemperature-based breakthrough detection system according to the presentdisclosure.

FIG. 11 is a schematic cross-sectional view of a portion of a PSAassembly that includes at least one adsorbent bed and atemperature-based breakthrough detection system according to the presentdisclosure.

FIG. 12 is a schematic cross-sectional view of a portion of a PSAassembly that includes at least one adsorbent bed and atemperature-based breakthrough detection system according to the presentdisclosure.

DETAILED DESCRIPTION AND BEST MODE OF THE DISCLOSURE

FIG. 1 illustrates schematically an example of an energy producing andconsuming assembly 56. The energy producing and consuming assembly 56includes an energy-producing system 22 and at least one energy-consumingdevice 52 adapted to exert an applied load on the energy-producingsystem 22. In the illustrated example, the energy-producing system 22includes a fuel cell stack 24 and a hydrogen-generation assembly 46.More than one of any of the illustrated components may be used withoutdeparting from the scope of the present disclosure. The energy-producingsystem may include additional components that are not specificallyillustrated in the schematic figures, such as air delivery systems, heatexchangers, sensors, controllers, flow-regulating devices, fuel and/orfeedstock delivery assemblies, heating assemblies, cooling assemblies,and the like. System 22 may also be referred to as a fuel cell system.

As discussed in more detail herein, hydrogen-generation assembliesand/or fuel cell systems according to the present disclosure include aseparation assembly that includes at least one pressure swing adsorption(PSA) assembly that is adapted to increase the purity of the hydrogengas that is produced in the hydrogen-generation assembly and/or consumedin the fuel cell stack. In a PSA process, gaseous impurities are removedfrom a stream containing hydrogen gas. PSA is based on the principlethat certain gases, under the proper conditions of temperature andpressure, will be adsorbed onto an adsorbent material more strongly thanother gases. These impurities may thereafter be desorbed and removed,such as in the form of a byproduct stream. The success of using PSA forhydrogen purification is due to the relatively strong adsorption ofcommon impurity gases (such as, but not limited to, CO, CO₂,hydrocarbons including CH₄, and N₂) on the adsorbent material. Hydrogenadsorbs only very weakly and so hydrogen passes through the adsorbentbed while the impurities are retained on the adsorbent material.

As discussed in more detail herein, a PSA process typically involvesrepeated, or cyclical, application of at least pressurization,separation (adsorption), depressurization (desorption), and purge steps,or processes, to selectively remove impurities from the hydrogen gas andthen desorb the impurities. Accordingly, the PSA process may bedescribed as being adapted to repeatedly enable a PSA cycle of steps, orstages, such as the above-described steps. The degree of separation isaffected by the pressure difference between the pressure of thereformate or other mixed gas stream that is delivered to the PSAassembly as a feed stream, and the pressure of the byproduct stream.Accordingly, the desorption step will typically include reducing thepressure within the portion of the PSA assembly containing the adsorbedgases, and optionally may even include drawing a vacuum (i.e., reducingthe pressure to less than atmospheric or ambient pressure) on thatportion of the assembly. Similarly, increasing the feed pressure of themixed gas stream to the adsorbent regions of the PSA assembly maybeneficially affect the degree of separation during the adsorption step.

As illustrated schematically in FIG. 1, the hydrogen-generation assembly46 includes at least a fuel processing system 64 and a feedstockdelivery system 58, as well as the associated fluid conduitsinterconnecting various components of the system. As used herein, theterm “hydrogen-generation assembly” may be used to refer to the fuelprocessing system 64 and associated components of the energy-producingsystem, such as feedstock delivery systems 58, heating assemblies,separation regions or devices, air delivery systems, fuel deliverysystems, fluid conduits, heat exchangers, cooling assemblies, sensorassemblies, flow regulators, controllers, etc. All of these illustrativecomponents are not required to be included in any hydrogen-generationassembly or used with any fuel processing system according to thepresent disclosure. Similarly, other components may be included or usedas part of the hydrogen-generation assembly.

Regardless of its construction or components, the feedstock deliverysystem 58 is adapted to deliver to the fuel processing system 64 one ormore feedstocks via one or more streams, which may be referred togenerally as feedstock supply stream(s) 68. In the following discussion,reference may be made only to a single feedstock supply stream, but iswithin the scope of the present disclosure that two or more suchstreams, of the same or different composition, may be used. In someembodiments, air may be supplied to the fuel processing system 64 via ablower, fan, compressor or other suitable air delivery system, and/or awater stream may be delivered from a separate water source.

Fuel processing system 64 includes any suitable device(s) and/orstructure(s) that are configured to produce hydrogen gas from thefeedstock supply stream(s) 68. As schematically illustrated in FIG. 1,the fuel processing system 64 includes a hydrogen-producing region 70.Accordingly, fuel processing system 64 may be described as including ahydrogen-producing region 70 that produces a hydrogen-rich stream 74that includes hydrogen gas as a majority component from the feedstocksupply stream. While stream 74 contains hydrogen gas as its majoritycomponent, it also contains other gases, and as such may be referred toas a mixed gas stream that contains hydrogen gas and other gases.Illustrative, non-exclusive examples of these other gases, orimpurities, include one or more of such illustrative impurities ascarbon monoxide, carbon dioxide, water, methane, and unreactedfeedstock.

Illustrative, non-exclusive examples of suitable mechanisms forproducing hydrogen gas from feedstock supply stream 68 include steamreforming and autothermal reforming, in which reforming catalysts areused to produce hydrogen gas from a feedstock supply stream 68containing water and at least one carbon-containing feedstock. Otherexamples of suitable mechanisms for producing hydrogen gas includepyrolysis and catalytic partial oxidation of a carbon-containingfeedstock, in which case the feedstock supply stream 68 does not containwater. Still another suitable mechanism for producing hydrogen gas iselectrolysis, in which case the feedstock is water. Illustrative,non-exclusive examples of suitable carbon-containing feedstocks includeat least one hydrocarbon or alcohol. Illustrative, non-exclusiveexamples of suitable hydrocarbons include methane, propane, natural gas,diesel, kerosene, gasoline, and the like. Illustrative, non-exclusiveexamples of suitable alcohols include methanol, ethanol, and polyols,such as ethylene glycol and propylene glycol.

The hydrogen-generation assembly 46 may utilize more than a singlehydrogen-producing mechanism in the hydrogen-producing region 70 and mayinclude more than one hydrogen-producing region. Each of thesemechanisms is driven by, and results in, different thermodynamicbalances in the hydrogen-generation assembly 46. Accordingly, thehydrogen-generation assembly 46 may further include a temperaturemodulating assembly 71, such as a heating assembly and/or a coolingassembly. The temperature modulating assembly 71 may be configured aspart of the fuel processing system 64 or may be an external componentthat is in thermal and/or fluid communication with thehydrogen-producing region 70. The temperature modulating assembly 71 mayconsume a fuel stream, such as to generate heat. While not required inall embodiments of the present disclosure, the fuel stream may bedelivered from the feedstock delivery system. For example, and asindicated in dashed lines in FIG. 1, this fuel, or feedstock, may bereceived from the feedstock delivery system 58 via a fuel supply stream69. The fuel supply stream 69 may include combustible fuel or,alternatively, may include fluids to facilitate cooling. The temperaturemodulating assembly 71 may also receive some or all of its feedstockfrom other sources or supply systems, such as from additional storagetanks. It may also receive the air stream from any suitable source,including the environment within which the assembly is used. Blowers,fans and/or compressors may be used to provide the air stream, but thisis not required to all embodiments.

The temperature modulating assembly 71 may include one or more heatexchangers, burners, combustion systems, and other such devices forsupplying heat to regions of the fuel processing system and/or otherportions of assembly 56. Depending on the configuration of thehydrogen-generation assembly 46, the temperature modulating assembly 71may also, or alternatively, include heat exchangers, fans, blowers,cooling systems, and other such devices for cooling regions of the fuelprocessing system 64 or other portions of assembly 56. For example, whenthe fuel processing system 64 is configured with a hydrogen-producingregion 70 based on steam reforming or another endothermic reaction, thetemperature modulating assembly 71 may include systems for supplyingheat to maintain the temperature of the hydrogen-producing region 70 andthe other components in the proper range.

When the fuel processing system is configured with a hydrogen-producingregion 70 based on catalytic partial oxidation or another exothermicreaction, the temperature modulating assembly 71 may include systems forremoving heat, i.e., supplying cooling, to maintain the temperature ofthe fuel processing system in the proper range. As used herein, the term“heating assembly” is used to refer generally to temperature modulatingassemblies that are configured to supply heat or otherwise increase thetemperature of all or selected regions of the fuel processing system. Asused herein, the term “cooling assembly” is used to refer generally totemperature moderating assemblies that are configured to cool, or reducethe temperature of, all or selected regions of the fuel processingsystem.

In FIG. 2, an illustrative, non-exclusive example of ahydrogen-generation assembly 46 is schematically illustrated. Asillustrated, the hydrogen-generation assembly includes fuel processingsystem 64, which includes a hydrogen-producing region 70 that is adaptedto produce mixed gas stream 74 by steam reforming one or more feedstocksupply streams 68 containing water 80 and at least one carbon-containingfeedstock 82. As illustrated, region 70 includes at least one reformingcatalyst bed 84 containing one or more suitable reforming catalysts 86.In the illustrative example, the hydrogen-producing region may bereferred to as a reforming region, and the mixed gas stream may bereferred to as a reformate stream.

As also shown in FIGS. 1 and 2, the mixed gas stream is adapted to bedelivered to a separation region, or assembly, 72 that includes at leastone PSA assembly 73. PSA assembly 73 separates the mixed gas (orreformate) stream into at least one product hydrogen stream 42 and atleast one byproduct stream 76. Product hydrogen stream 42 contains atleast one of a greater concentration of hydrogen gas and a lowerconcentration of the other gases than the mixed gas stream. Byproductstream 76 contains at least a substantial portion of the impurities, orother gases, present in mixed gas stream 74. Byproduct stream 76 maycontain no hydrogen gas, but it typically will contain some hydrogengas, such as in a reduced concentration than was present in the mixedgas stream. While not required, it is within the scope of the presentdisclosure that fuel processing system 64 may be adapted to produce oneor more byproduct streams containing sufficient amounts of hydrogen(and/or other) gas(es) to be suitable for use as a fuel, or feedstock,stream for a heating assembly for the fuel processing system. In someembodiments, the byproduct stream may have sufficient fuel value (i.e.,hydrogen and/or other combustible gas content) to enable the heatingassembly, when present, to maintain the hydrogen-producing region at adesired operating (i.e., hydrogen-producing) temperature or within aselected range of temperatures.

As illustrated in FIG. 2, the hydrogen-generation assembly includes atemperature modulating assembly in the form of a heating assembly 71that is adapted to produce a heated exhaust stream 88 that is adapted toheat at least the reforming region of the hydrogen-generation assembly.It is within the scope of the present disclosure that stream 88 may beused to heat other portions of the hydrogen-generation assembly and/orenergy-producing system 22.

As indicated in dashed lines in FIGS. 1 and 2, it is within the scope ofthe present disclosure that the byproduct stream from the PSA assemblymay form at least a portion of the fuel stream for the heating assembly.Also shown in FIG. 2 are air stream 90, which may be delivered from anysuitable air source, and fuel stream 92, which contains any suitablecombustible fuel suitable for being combusted with air in the heatingassembly. Fuel stream 92 may be used as the sole fuel stream for theheating assembly, but as discussed, it is also within the scope of thedisclosure that other combustible fuel streams may be used, such as thebyproduct stream from the PSA assembly, the anode exhaust stream from afuel cell stack, etc. When the byproduct or exhaust streams from othercomponents of system 22 have sufficient fuel value, fuel stream 92 maynot be used. When they do not have sufficient fuel value, are used forother purposes, or are not being generated, fuel stream 92 may be usedinstead or in combination.

Illustrative, non-exclusive examples of suitable fuels include one ormore of the above-described carbon-containing feedstocks, althoughothers may be used. As an illustrative example of temperatures that maybe achieved and/or maintained in hydrogen-producing region 70 throughthe use of heating assembly 71, steam reformers typically operate attemperatures in the range of 200° C. and 900° C. Temperatures outside ofthis range are within the scope of the disclosure. When thecarbon-containing feedstock is methanol, the steam reforming reactionwill typically operate in a temperature range of approximately 200-500°C. Illustrative subsets of this range include 350-450° C., 375-425° C.,and 375-400° C. When the carbon-containing feedstock is a hydrocarbon,ethanol, or a similar alcohol, a temperature range of approximately400-900° C. will typically be used for the steam reforming reaction.Illustrative subsets of this range include 750-850° C., 650-750° C.,700-800° C., 700-900° C., 500-800° C., 400-600° C., and 600-800° C.

It is within the scope of the present disclosure that the separationregion may be implemented within system 22 anywhere downstream from thehydrogen-producing region and upstream from the fuel cell stack. In theillustrative example shown schematically in FIG. 1, the separationregion is depicted as part of the hydrogen-generation assembly, but thisconstruction is not required. It is also within the scope of the presentdisclosure that the hydrogen-generation assembly may utilize a chemicalor physical separation process in addition to PSA assembly 73 to removeor reduce the concentration of one or more selected impurities from themixed gas stream. When separation assembly 72 utilizes a separationprocess in addition to PSA, the one or more additional processes may beperformed at any suitable location within system 22 and are not requiredto be implemented with the PSA assembly. An illustrative, non-exclusiveexample of a chemical separation process is the use of a methanationcatalyst to selectively reduce the concentration of carbon monoxidepresent in stream 74. Other illustrative chemical separation processesinclude partial oxidation of carbon monoxide to form carbon dioxide andwater-gas shift reactions to produce hydrogen gas and carbon dioxidefrom water and carbon monoxide. Illustrative, non-exclusive examples ofphysical separation processes include the use of a physical membrane orother barrier adapted to permit the hydrogen gas to flow therethroughbut adapted to prevent at least selected impurities from passingtherethrough. These membranes may be referred to as beinghydrogen-selective membranes. Illustrative, non-exclusive examples ofsuitable membranes are formed from palladium or a palladium alloy andare disclosed in the references incorporated herein.

Hydrogen-generation assembly 46 preferably is adapted to produce atleast substantially pure hydrogen gas, and even more preferably, thehydrogen-generation assembly is adapted to produce pure hydrogen gas.For the purposes of the present disclosure, a stream containingsubstantially pure hydrogen gas may refer to a stream containinghydrogen gas that is greater than 90% pure, greater than 95% pure,greater than 99% pure, greater than 99.5%, or even at least 99.9% pure.Illustrative, nonexclusive examples of suitable fuel processing systemsare disclosed in U.S. Pat. Nos. 6,221,117, 5,997,594, 5,861,137, andpending U.S. Patent Application Publication Nos. 2001/0045061,2003/0192251, and 2003/0223926. The complete disclosures of theabove-identified patents and patent applications are hereby incorporatedby reference for all purposes.

Hydrogen from the fuel processing system 64 may be delivered to one ormore of a hydrogen storage device 62 and the fuel cell stack 24 viaproduct hydrogen stream 42. Some or all of hydrogen stream 42 mayadditionally, or alternatively, be delivered, via a suitable conduit,for use in another hydrogen-consuming process, burned for fuel or heat,or stored for later use. With reference to FIG. 1, the hydrogen gas usedas a proton source, or reactant, for fuel cell stack 24 may be deliveredto the stack from one or more of fuel processing system 64 and storagedevice 62. Fuel cell stack 24 includes at least one fuel cell 20, andtypically includes a plurality of fluidly and electricallyinterconnected fuel cells. When these cells are connected together inseries, the power output of the fuel cell stack is the sum of the poweroutputs of the individual cells. The cells in stack 24 may be connectedin series, parallel, or combinations of series and parallelconfigurations.

FIG. 3 illustrates schematically a fuel cell 20, one or more of whichmay be configured to form fuel cell stack 24. The fuel cell stacks ofthe present disclosure may utilize any suitable type of fuel cell, andpreferably fuel cells that receive hydrogen and oxygen as proton sourcesand oxidants. Illustrative, non-exclusive examples of types of fuelcells include proton exchange membrane (PEM) fuel cells, alkaline fuelcells, solid oxide fuel cells, molten carbonate fuel cells, phosphoricacid fuel cells, and the like. For the purpose of illustration, anexemplary fuel cell 20 in the form of a PEM fuel cell is schematicallyillustrated in FIG. 3.

Proton exchange membrane fuel cells typically utilize amembrane-electrode assembly 26 consisting of an ion exchange, orelectrolytic, membrane 29 located between an anode region 30 and acathode region 32. Each region 30 and 32 includes an electrode 34,namely an anode 36 and a cathode 38, respectively. Each region 30 and 32also includes a support 39, such as a supporting plate 40. Support 39may form a portion of a monopolar or bipolar plate, or plate assembly.The supporting plates 40 of fuel cells 20 carry the relative voltagepotentials produced by the fuel cells.

In operation, hydrogen gas from product stream 42 is delivered to theanode region, and oxidant 44 is delivered to the cathode region. Atypical, but not exclusive, oxidant is oxygen. As used herein, hydrogenrefers to hydrogen gas and oxygen refers to oxygen gas. The followingdiscussion will refer to hydrogen as the proton source, or fuel, for thefuel cell (stack), and oxygen as the oxidant, although it is within thescope of the present disclosure that other fuels and/or oxidants may beused. Hydrogen and oxygen 44 may be delivered to the respective regionsof the fuel cell via any suitable mechanism from respective sources 46and 48. Illustrative examples of suitable sources 48 of oxygen 44include a pressurized tank of oxygen or air, or a fan, compressor,blower or other device for directing air to the cathode region.

Hydrogen and oxygen typically combine with one another via anoxidation-reduction reaction. Although membrane 29 restricts the passageof a hydrogen molecule, it will permit a hydrogen ion (proton) to passthrough it, largely due to the ionic conductivity of the membrane. Thefree energy of the oxidation-reduction reaction drives the proton fromthe hydrogen gas through the ion exchange membrane. As membrane 29 alsotends not to be electrically conductive, an external circuit 50 is thelowest energy path for the remaining electron, and is schematicallyillustrated in FIG. 3. In cathode region 32, electrons from the externalcircuit and protons from the membrane combine with oxygen to producewater and heat.

Also shown in FIG. 3 are an anode purge, or exhaust, stream 54, whichmay contain hydrogen gas, and a cathode air exhaust stream 55, which istypically at least partially, if not substantially, depleted of oxygen.Fuel cell stack 24 may include a common hydrogen (or other reactant)feed, air intake, and stack purge and exhaust streams, and accordinglywill include suitable fluid conduits to deliver the associated streamsto, and collect the streams from, the individual fuel cells. Similarly,any suitable mechanism may be used for selectively purging the regions.

In practice, a fuel cell stack 24 will typically contain a plurality offuel cells with bipolar plate assemblies separating adjacentmembrane-electrode assemblies. The bipolar plate assemblies essentiallypermit the free electron to pass from the anode region of a first cellto the cathode region of the adjacent cell via the bipolar plateassembly, thereby establishing an electrical potential through the stackthat may be used to satisfy an applied load. This net flow of electronsproduces an electric current that may be used to satisfy an appliedload, such as from at least one of an energy-consuming device 52 and theenergy-producing system 22.

For a constant output voltage, such as 12 volts or 24 volts, the outputpower may be determined by measuring the output current. The electricaloutput may be used to satisfy an applied load, such as fromenergy-consuming device 52. FIG. 1 schematically depicts thatenergy-producing system 22 may include at least one energy-storagedevice 78. Device 78, when included, may be adapted to store at least aportion of the electrical output, or power, 79 from the fuel cell stack24. An illustrative, non-exclusive example of a suitable energy-storagedevice 78 is a battery, but others may be used. Energy-storage device 78may additionally or alternatively be used to power the energy-producingsystem 22 during start-up of the system.

The at least one energy-consuming device 52 may be electrically coupledto the energy-producing system 22, such as to the fuel cell stack 24and/or one or more energy-storage devices 78 associated with the stack.Device 52 applies a load to the energy-producing system 22 and draws anelectric current from the system to satisfy the load. This load may bereferred to as an applied load, and may include thermal and/orelectrical load(s). It is within the scope of the present disclosurethat the applied load may be satisfied by the fuel cell stack, theenergy-storage device, or both the fuel cell stack and theenergy-storage device. Illustrative, non-exclusive examples of devices52 include motor vehicles, recreational vehicles, boats and other seacraft, and any combination of one or more residences, commercial officesor buildings, neighborhoods, tools, lights and lighting assemblies,appliances, computers, industrial equipment, signaling andcommunications equipment, radios, electrically powered components onboats, recreational vehicles or other vehicles, battery chargers andeven the balance-of-plant electrical requirements for theenergy-producing system 22 of which fuel cell stack 24 forms a part.

As indicated in dashed lines at 77 in FIG. 1, the energy-producingsystem may, but is not required to, include at least one powermanagement module 77. Power management module 77 includes any suitablestructure for conditioning or otherwise regulating the electricityproduced by the energy-producing system, such as for delivery toenergy-consuming device 52. Module 77 may include such illustrativestructure as buck or boost converters, inverters, power filters, and thelike.

In FIG. 4 an illustrative example of a PSA assembly 73 is shown. Asshown, assembly 73 includes a plurality of adsorbent beds 100 that arefluidly connected via distribution assemblies 102 and 104. Beds 100 mayadditionally or alternatively be referred to as adsorbent chambers oradsorption regions. The distribution assemblies have been schematicallyillustrated in FIG. 4 and may include any suitable structure forselectively establishing and restricting fluid flow between the bedsand/or the input and output streams of assembly 73. As shown, the inputand output streams include at least mixed gas stream 74, producthydrogen stream 42, and byproduct stream 76. Illustrative examples ofsuitable structures include one or more manifolds, such as distributionand collection manifolds that are respectively adapted to distributefluid to and collect fluid from the beds, and valves, such as checkvalves, solenoid valves, purge valves, and the like. In the illustrativeexample, three beds 100 are shown, but it is within the scope of thepresent disclosure that the number of beds may vary, such as to includemore or fewer beds than shown in FIG. 4. While assembly 73 couldtechnically contain only a single bed, assembly 73 typically willinclude at least two beds, and often will include three, four, or morebeds. While not required, assembly 73 is preferably adapted to provide acontinuous flow of product hydrogen stream, with at least one of theplurality of beds exhausting this stream when the assembly is in use andreceiving a continuous flow of mixed gas stream 74.

In the illustrative example, distribution assembly 102 is adapted toselectively deliver mixed gas stream 74 to the plurality of beds and tocollect and exhaust byproduct stream 76, and distribution assembly 104is adapted to collect the purified hydrogen gas that passes through thebeds and which forms product hydrogen stream 42, and in some embodimentsto deliver a portion of the purified hydrogen gas to the beds for use asa purge stream. The distribution assemblies may be configured for fixedor rotary positioning relative to the beds. Furthermore, thedistribution assemblies may include any suitable type and number ofstructures and devices to selectively distribute, regulate, meter,prevent and/or collect flows of the corresponding gas streams. Asillustrative, non-exclusive examples, distribution assembly 102 mayinclude mixed gas and exhaust manifolds, or manifold assemblies, anddistribution assembly 104 may include product and purge manifolds, ormanifold assemblies. In practice, PSA assemblies that utilizedistribution assemblies that rotate relative to the beds may be referredto as rotary pressure swing adsorption assemblies, and PSA assemblies inwhich the manifolds and beds are not adapted to rotate relative to eachother to selectively establish and restrict fluid connections may bereferred to as fixed bed, or discrete bed, pressure swing adsorptionassemblies. Both constructions are within the scope of the presentdisclosure.

Gas purification by pressure swing adsorption involves sequentialpressure cycling and flow reversal of gas streams relative to theadsorbent beds. In the context of purifying a mixed gas stream comprisedsubstantially of hydrogen gas, the mixed gas stream is delivered underrelatively high pressure to one end of the adsorbent beds and therebyexposed to the adsorbent(s) contained in the adsorbent region thereof.Illustrative, non-exclusive examples of delivery pressures for mixed gasstream 74 include pressures in the range of 40-200 psi, such aspressures in the range of 50-150 psi, 50-100 psi, 100-150 psi, 70-100psi, etc., although pressures outside of this range are within the scopeof the present disclosure. As the mixed gas stream flows through theadsorbent region, carbon monoxide, carbon dioxide, water and/or otherones of the impurities, or other gases, are adsorbed, and thereby atleast temporarily retained, on the adsorbent due to the fact that thesegases are more readily adsorbed on the selected adsorbents used in thePSA assembly than hydrogen gas. The remaining portion of the mixed gasstream, which now may perhaps more accurately be referred to as apurified hydrogen stream, passes through the bed and is exhausted fromthe other end of the bed. In this context, hydrogen gas may be describedas being the less readily adsorbed component of the mixed gas stream,while carbon monoxide, carbon dioxide, etc. may be described as the morereadily adsorbed components of the mixed gas stream. The pressure of theproduct hydrogen stream is typically reduced prior to utilization of thegas by the fuel cell stack.

To remove the adsorbed gases, the flow of the mixed gas stream isstopped, the pressure in the bed is reduced, and the now desorbed gasesare exhausted from the bed. The desorption step often includesselectively decreasing the pressure within the adsorbent region throughthe withdrawal of gas, typically in a countercurrent direction relativeto the feed direction. This desorption step may also be referred to as adepressurization, or blowdown, step. This step often includes or isperformed in conjunction with the use of a purge gas stream, which istypically delivered in a countercurrent flow direction to the directionat which the mixed gas stream flows through the adsorbent region. Anillustrative, non-exclusive example of a suitable purge gas stream is aportion of the product hydrogen stream, as this stream is comprised ofhydrogen gas, which is less readily adsorbed than the adsorbed gases.Other gases may be used in the purge gas stream, although these gasespreferably are less readily adsorbed than the adsorbed gases, and evenmore preferably are not adsorbed, or are only weakly adsorbed, on theadsorbent(s) being used.

As discussed, this desorption step may include drawing an at leastpartial vacuum on the bed, but this is not required. While not required,it is often desirable to utilize one or more equalization steps, inwhich two or more beds are fluidly interconnected to permit the beds toequalize the relative pressures therebetween. For example, one or moreequalization steps may precede the desorption and pressurization steps.Prior to the desorption step, equalization is used to reduce thepressure in the bed and to recover some of the purified hydrogen gascontained in the bed, while prior to the (re)pressurization step,equalization is used to increase the pressure within the bed.Equalization may be accomplished using cocurrent and/or countercurrentflow of gas. After the desorption and/or purge step(s) of the desorbedgases is completed, the bed is again pressurized and ready to againreceive and remove impurities from the portion of the mixed gas streamdelivered thereto.

For example, when a bed is ready to be regenerated, it is typically at arelatively high pressure and contains a quantity of hydrogen gas. Whilethis gas (and pressure) may be removed simply by venting the bed, otherbeds in the assembly will need to be pressurized prior to being used topurify the portion of the mixed gas stream delivered thereto.Furthermore, the hydrogen gas in the bed to be regenerated preferably isrecovered so as to not negatively impact the efficiency of the PSAassembly. Therefore, interconnecting these beds in fluid communicationwith each other permits the pressure and hydrogen gas in the bed to beregenerated to be reduced while also increasing the pressure andhydrogen gas in a bed that will be used to purify impure hydrogen gas(i.e., mixed gas stream 74) that is delivered thereto. In addition to,or in place of, one or more equalization steps, a bed that will be usedto purify the mixed gas stream may be pressurized prior to the deliveryof the mixed gas stream to the bed. For example, some of the purifiedhydrogen gas may be delivered to the bed to pressurize the bed. While itis within the scope of the present disclosure to deliver thispressurization gas to either end of the bed, in some embodiments it maybe desirable to deliver the pressurization gas to the opposite end ofthe bed than the end to which the mixed gas stream is delivered.

The above discussion of the general operation of a PSA assembly has beensomewhat simplified. Illustrative examples of pressure swing adsorptionassemblies, including components thereof and methods of operating thesame, are disclosed in U.S. Pat. Nos. 3,564,816, 3,986,849, 5,441,559,6,692,545, and 6,497,856, the complete disclosures of which are herebyincorporated by reference for all purposes.

In FIG. 5, an illustrative example of an adsorbent bed 100 isschematically illustrated. As shown, the bed defines an internalcompartment 110 that contains at least one adsorbent 112, with eachadsorbent being adapted to adsorb one or more of the components of themixed gas stream. It is within the scope of the present disclosure thatmore than one adsorbent may be used. For example, a bed may include morethan one adsorbent adapted to adsorb a particular component of the mixedgas stream, such as to adsorb carbon monoxide, and/or two or moreadsorbents that are each adapted to adsorb a different component of themixed gas stream. Similarly, an adsorbent may be adapted to adsorb twoor more components of the mixed gas stream. Illustrative, non-exclusiveexamples of suitable adsorbents include activated carbon, alumina andzeolite adsorbents. An additional example of an adsorbent that may bepresent within the adsorbent region of the beds is a desiccant that isadapted to adsorb water present in the mixed gas stream. Illustrativedesiccants include silica and alumina gels. When two or more adsorbentsare utilized, they may be sequentially positioned (in a continuous ordiscontinuous relationship) within the bed or may be mixed together. Itshould be understood that the type, number, amount, and form ofadsorbent in a particular PSA assembly may vary, such as according toone or more of the following factors: the operating conditions expectedin the PSA assembly, the size of the adsorbent bed, the compositionand/or properties of the mixed gas stream, the desired application forthe product hydrogen stream produced by the PSA assembly, the operatingenvironment in which the PSA assembly will be used, user preferences,durability of the adsorbent, cost of the adsorbent, etc.

When the PSA assembly includes a desiccant or other water-removalcomposition or device, it may be positioned to remove water from themixed gas stream prior to adsorption of other impurities from the mixedgas stream. One reason for this is that water may negatively affect theability of some adsorbents to adsorb other components of the mixed gasstream, such as carbon monoxide. An illustrative, non-exclusive exampleof a water-removal device is a condenser, but others may be used betweenthe hydrogen-producing region and adsorbent region, as schematicallyillustrated in dashed lines at 122 in FIG. 1. For example, at least oneheat exchanger, condenser, or other suitable water-removal device may beused to cool the mixed gas stream prior to delivery of the stream to thePSA assembly. This cooling may condense some of the water present in themixed gas stream. Continuing this example, and to provide a morespecific illustration, mixed gas streams produced by steam reformerstend to contain at least 10%, and often at least 15% or more water whenexhausted from the hydrogen-producing (i.e., the reforming) region ofthe fuel processing system. These streams also tend to be fairly hot,such as having a temperature of at least 300° C. (in the case of manymixed gas streams produced from methanol or similar carbon-containingfeedstocks), and at least 600-800° C. (in the case of many mixed gasstreams produced from natural gas, propane or similar carbon-containingfeedstocks). When cooled prior to delivery to the PSA assembly, such asto an illustrative temperature in the range of 25-100° C. or even 40-80°C., most of this water will condense. The mixed gas stream may still besaturated with water, but the water content will tend to be less than 5wt %.

The adsorbent(s) may be present in the bed in any suitable form,illustrative examples of which include particulate form, bead form,porous discs or blocks, coated structures, laminated sheets, fabrics,and the like. When positioned for use in the beds, the adsorbents shouldprovide sufficient porosity and/or gas flow paths for the non-adsorbedportion of the mixed gas stream to flow through the bed withoutsignificant pressure drop through the bed. As used herein, the portionof a bed that contains adsorbent will be referred to as the adsorbentregion of the bed. In FIG. 5, an adsorbent region is indicated generallyat 114. Beds 100 also may (but are not required to) include partitions,supports, screens and other suitable structure for retaining theadsorbent and other components of the bed within the compartment, inselected positions relative to each other, in a desired degree ofcompression, etc. These devices are generally referred to as supportsand are generally indicated in FIG. 5 at 116. Therefore, it is withinthe scope of the present disclosure that the adsorbent region maycorrespond to the entire internal compartment of the bed, or only asubset thereof. Similarly, the adsorbent region may be comprised of acontinuous region or two or more spaced apart regions without departingfrom the scope of the present disclosure.

In the illustrated example shown in FIG. 5, bed 100 includes at leastone port 118 associated with each end region of the bed. As indicated indashed lines, it is within the scope of the present disclosure thateither or both ends of the bed may include more than one port.Similarly, it is within the scope of the disclosure that the ports mayextend laterally from the beds or otherwise have a different geometrythan the schematic examples shown in FIG. 5. Regardless of theconfiguration and/or number of ports, the ports are collectively adaptedto deliver fluid for passage through the adsorbent region of the bed andto collect fluid that passes through the adsorbent region. As discussed,the ports may selectively, such as depending upon the particularimplementation of the PSA assembly and/or stage in the PSA cycle, beused as an input port or an output port. For the purpose of providing agraphical example, FIG. 6 illustrates a bed 100 in which the adsorbentregion extends along the entire length of the bed, i.e., between theopposed ports or other end regions of the bed. In FIG. 7, bed 100includes an adsorbent region 114 that includes discontinuous subregions120.

During use of an adsorbent bed, such as bed 100, to adsorb impuritygases (namely the gases with greater affinity for being adsorbed by theadsorbent), a mass-transfer zone will be defined in the adsorbentregion. More particularly, adsorbents have a certain adsorptioncapacity, which is defined at least in part by the composition of themixed gas stream, the flow rate of the mixed gas stream, the operatingtemperature and/or pressure at which the adsorbent is exposed to themixed gas stream, any adsorbed gases that have not been previouslydesorbed from the adsorbent, etc. As the mixed gas stream is deliveredto the adsorbent region of a bed, the adsorbent at the end portion ofthe adsorbent region proximate the mixed gas delivery port will removeimpurities from the mixed gas stream. Generally, these impurities willbe adsorbed within a subset of the adsorbent region, and the remainingportion of the adsorbent region downstream from this subset will haveonly minimal, if any, adsorbed impurity gases. In the context of gasflow through the adsorbent beds, upstream and downstream respectivelyrefer to portions of the beds (or adjacent structure) that have alreadybeen passed by, or which have yet to be passed by, the gas in the regionfrom which this measurement is made. In FIG. 8, adsorbent region 114 issomewhat schematically shown including a mass transfer zone, or region,130.

As the adsorbent in the initial mass transfer zone continues to adsorbimpurities, it will near or even reach its capacity for adsorbing theseimpurities. As this occurs, the mass transfer zone will move toward theopposite end of the adsorbent region. More particularly, as the flow ofimpurity gases exceeds the capacity of a particular portion of theadsorbent region (i.e., a particular mass transfer zone) to adsorb thesegases, the gases will flow beyond that region and into the adjoining(downstream) portion of the adsorbent region, where they will beadsorbed by the adsorbent in that portion, effectively expanding and/ormoving the mass transfer zone generally toward the opposite end of thebed.

This description is somewhat simplified in that the mass transfer zoneoften does not define uniform beginning and ending boundaries along theadsorbent region, especially when the mixed gas stream contains morethan one gas that is adsorbed by the adsorbent. Similarly, these gasesmay have different affinities for being adsorbed and therefore may evencompete with each other for adsorbent sites. However, a substantialportion (such as at least 70% or more) of the adsorption will tend tooccur in a relatively localized portion of the adsorbent region, withthis portion, or zone, tending to migrate from the feed end to theproduct end of the adsorbent region during use of the bed. This isschematically illustrated in FIG. 9, in which mass transfer zone 130 isshown moved toward port 118′ relative to its position in FIG. 8.Accordingly, the adsorbent 112′ in portion 114′ of the adsorbent regionwill have a substantially reduced capacity, if any, to adsorb additionalimpurities from the mixed gas stream. Described in other terms,adsorbent 112′ may be described as being substantially, if notcompletely, saturated with adsorbed gases. In FIGS. 8 and 9, the feedand product ends of the adsorbent region are generally indicated at 124and 126 and generally refer to the portions of the adsorbent region thatare proximate, or closest to, the mixed gas delivery port and theproduct port of the bed.

During use of the PSA assembly, the mass transfer zone will tend tomigrate toward and away from ends 124 and 126 of the adsorbent region.More specifically, and as discussed, PSA is a cyclic process thatinvolves repeated changes in pressure and flow direction. The followingdiscussion will describe the PSA cycle with reference to how steps inthe cycle tend to affect the mass transfer zone (and/or the distributionof adsorbed gases through the adsorbent region). It should be understoodthat the size, or length, of the mass transfer zone will tend to varyduring use of the PSA assembly, and therefore tends not to be of a fixeddimension.

At the beginning of a PSA cycle, the bed is pressurized and the mixedgas stream flows under pressure through the adsorbent region. Duringthis adsorption step, impurities (i.e., the other gases) are adsorbed bythe adsorbent(s) in the adsorbent region. As these impurities areadsorbed, the mass transfer zone tends to move toward the distal, orproduct, end of the adsorbent region as initial portions of theadsorbent region become more and more saturated with adsorbed gas. Whenthe adsorption step is completed, the flow of mixed gas stream 74 to theadsorbent bed and the flow of purified hydrogen gas (at least a portionof which will form product hydrogen stream 42) are stopped. While notrequired, the bed may then undergo one or more equalization steps inwhich the bed is fluidly interconnected with one or more other beds inthe PSA assembly to decrease the pressure and hydrogen gas present inthe bed and to charge the receiving bed(s) with pressure and hydrogengas. Gas may be withdrawn from the pressurized bed from either, or bothof, the feed or the product ports. Drawing the gas from the product portwill tend to provide hydrogen gas of greater purity than gas drawn fromthe feed port. However, the decrease in pressure resulting from thisstep will tend to draw impurities in the direction at which the gas isremoved from the adsorbent bed. Accordingly, the mass transfer zone maybe described as being moved toward the end of the adsorbent bed closestto the port from which the gas is removed from the bed. Expressed indifferent terms, when the bed is again used to adsorb impurities fromthe mixed gas stream, the portion of the adsorbent region in which themajority of the impurities are adsorbed at a given time, i.e., the masstransfer zone, will tend to be moved toward the feed or product end ofthe adsorbent region depending upon the direction at which theequalization gas is withdrawn from the bed.

The bed is then depressurized, with this step typically drawing gas fromthe feed port because the gas stream will tend to have a higherconcentration of the other gases, which are desorbed from the adsorbentas the pressure in the bed is decreased. This exhaust stream may bereferred to as a byproduct, or impurity, stream 76 and may be used for avariety of applications, including as a fuel stream for a burner orother heating assembly that combusts a fuel stream to produce a heatedexhaust stream. As discussed, hydrogen-generation assembly 46 mayinclude a heating assembly 71 that is adapted to produce a heatedexhaust stream to heat at least the hydrogen-producing region 70 of thefuel processing system. According to Henry's Law, the amount of adsorbedgases that are desorbed from the adsorbent is related to the partialpressure of the adsorbed gas present in the adsorbent bed. Therefore,the depressurization step may include, be followed by, or at leastpartially overlap in time with, a purge step, in which gas, typically atlow pressure, is introduced into the adsorbent bed. This gas flowsthrough the adsorbent region and draws the desorbed gases away from theadsorbent region, with this removal of the desorbed gases resulting infurther desorption of gas from the adsorbent. As discussed, a suitablepurge gas is purified hydrogen gas, such as previously produced by thePSA assembly. Typically, the purge stream flows from the product end tothe feed end of the adsorbent region to urge the impurities (and thusreposition the mass transfer zone) toward the feed end of the adsorbentregion. It is within the scope of the disclosure that the purge gasstream may form a portion of the byproduct stream, may be used as acombustible fuel stream (such as for heating assembly 71), and/or may beotherwise utilized in the PSA or other processes.

The illustrative, non-exclusive example of a PSA cycle is now completed,and a new cycle is typically begun. For example, the purged adsorbentbed is then repressurized, such as by being a receiving bed for anotheradsorbent bed undergoing equalization, and optionally may be furtherpressurized by purified hydrogen gas delivered thereto. By utilizing aplurality of adsorbent beds, typically three or more, the PSA assemblymay be adapted to receive a continuous flow of mixed gas stream 74 andto produce a continuous flow of purified hydrogen gas (i.e., acontinuous flow of product hydrogen stream 42). While not required, thetime for the adsorption step, or stage, often represents one-third totwo-thirds of the PSA cycle, such as representing approximately half ofthe time for a PSA cycle.

It is typically desirable to stop the adsorption step before the masstransfer zone reaches the distal end (relative to the direction at whichthe mixed gas stream is delivered to the adsorbent region) of theadsorbent region. In other words, the flow of mixed gas stream 74 andthe removal of product hydrogen stream 42 preferably should be stoppedbefore the other gases that are desired to be removed from the hydrogengas are exhausted from the bed with the hydrogen gas because theadsorbent is saturated with adsorbed gases and therefore can no longereffectively prevent these impurity gases from being exhausted in whatdesirably is a purified hydrogen stream. This contamination of theproduct hydrogen stream with impurity gases that desirably are removedby the PSA assembly may be referred to as breakthrough, in that theimpurity gases “break through” the adsorbent region of the bed.Conventionally, carbon monoxide detectors have been used to determinewhen the mass transfer zone is nearing or has reached the distal end ofthe adsorbent region and thereby is, or will, be present in the producthydrogen stream. Carbon monoxide detectors are used more commonly thandetectors for other ones of the other gases present in the mixed gasstream because carbon monoxide can damage many fuel cells when presentin even a few parts per million (ppm). While effective, and within thescope of the present disclosure, this detection mechanism requires theuse of carbon monoxide detectors and related detection equipment, whichtends to be expensive and increase the complexity of the PSA assembly.

At least in the case of hydrogen purification by pressure swingadsorption, it has been discovered that the adsorbent tends to be hotterin the mass transfer zone than in other portions of the adsorbentregion, such as regions upstream, and especially downstream, from themass transfer zone. This is due to the heat of adsorption of theadsorbed gases. This temperature differential may vary by such factorsas the flow rate of the mixed gas stream, the type of adsorbent, the gasbeing adsorbed, the packing or other form of the adsorbent, etc., butthe differential should be at least a few degrees Celsius. For example,the temperature differential may be at least 1° C., at least 2° C., atleast 3° C., at least 5° C., or more. As discussed in more detailherein, system 140 may also be referred to as a temperature assemblythat is adapted to measure the temperature of the adsorbent in at leastone location, and preferably two or more locations, within or associatedwith the adsorbent region and to control the operation of the PSAassembly responsive at least in part thereto.

Returning to FIG. 4, it is schematically illustrated that PSA assembliesaccording to the present disclosure include a temperature-basedbreakthrough detection system 140 associated with each of the beds thatwill be used to purify mixed gas stream 74. System 140 is adapted todetect the temperature of the adsorbent (directly or indirectly) in atleast one portion of the adsorbent region of each bed 100. As such,system 140 includes at least one temperature sensor, or detector, 142that is adapted to detect the temperature in, or is associated with, aportion of the adsorbent region of each bed, and at least one controller144 adapted to control the operation of the PSA assembly, and optionallyadditional portions of the hydrogen-generation assembly and/or fuel cellsystem, responsive at least in part thereto. System 140 may also bereferred to as a temperature-based breakthrough prevention system and/ora temperature-based control system, in that it is adapted to detect whenthe adsorbent bed is nearing and/or in a breakthrough condition and tocontrol the operation of at least PSA assembly 73 responsive thereto toprevent breakthrough, or further breakthrough, from occurring. As usedherein, the term “breakthrough condition” refers to when the masstransfer zone of the adsorbent region is present in a distal, orproduct, end portion, or subregion, of the adsorbent region. This endportion may include a selected percentage of the adsorbent region, suchas the final third, or subsets thereof, such as 30%, 25%, 20%, 15%, 10%,5%, or less, of the adsorbent region (i.e., the portion of the adsorbentregion closest to the product port). In other terms, a breakthroughcondition occurs when a substantial portion of the adsorption of atleast one of the other gases occurs in the distal (i.e. away from thefeed port) end portion of the adsorbent region. As discussed herein,system 140 is adapted to detect a breakthrough condition by detectingthe temperature of at least a portion of the adsorbent in the adsorbentregion and comparing this temperature to a reference temperature.

Temperature sensor 142 may include any suitable device or mechanismadapted to detect (directly or indirectly) the temperature of adsorbentwithin a selected portion of the adsorbent region. Thermocouples are anillustrative, non-exclusive example of a suitable device. In FIG. 10,only a single temperature sensor 142 is shown. It is within the scope ofthe present disclosure that more than one sensor may be utilized. Forexample, in FIG. 11, an illustrative bed 100 is shown with a pluralityof temperature sensors 142 spaced along the length of the adsorbentregion. As illustrated, a series of seven temperature sensors are shownand spaced along the length of the adsorbent region. It is within thescope of the present disclosure that more or fewer sensors may be used,including using more than one sensor to detect the temperature at agiven position along the length of the adsorbent region. While notrequired for the detection of a breakthrough condition or otherimpending passage of impurities through the adsorbent region, having oneor more temperature sensors located along the intermediate region of thebed and/or the feed end region of the bed may be desirable in someembodiments, such as to enable system 140 to determine the relativelocation of the mass transfer zone within the bed instead of simplydetermining whether the mass transfer zone is within a distal endportion of the adsorbent region.

As also illustrated in FIG. 12, it is also within the scope of thepresent disclosure to include at least one temperature sensor associatedwith a portion of the bed outside of the adsorbent region and/orassociated with one or more of ports 118, such as to detect thetemperature of the gas flowing into and/or out of the adsorbent bed,including but not limited to the gas upstream or downstream of theadsorbent bed. By “associated with” it is meant that the temperaturesensor may detect the actual temperature of the adsorbent or otherstructure whose temperature is desired to be measured, but thistemperature may also be indirectly measured. An example of an indirectmeasurement is measuring the temperature of adjacent structure. In sucha configuration, the actual temperature of the adsorbent or otherstructure may not be known, but the measured temperature will correspondgenerally to the actual temperature, and thereby may be used as anindirect, or relative, measurement of the desired temperature. Anotherexample is to measure or otherwise detect a value that is proportionalto the temperature to be measured. For example, when a thermocouple isused as a temperature sensor, the output from the thermocouple is avoltage, and the detected voltages, including relative differencesand/or changes thereto, may be used. As a further example, when aresistor is used to detect a temperature, the measured resistance of theresistor is proportional to the temperature.

In FIGS. 10-12, bed 100 is schematically illustrated, and it is withinthe scope of the present disclosure that any suitable construction maybe utilized, including those discussed, incorporated and/or illustratedherein. Similarly, sensors 142 have been graphically illustrated inFIGS. 10-12 extending partially within and partially outside of bed 100to schematically represent that the sensors may be located at anysuitable position relative to the adsorbent or other structure to bemeasured. For example, this may include positions in which a portion ofthe sensor extends in direct contact with the adsorbent or otherstructure within the bed and/or positions in which the sensor ispositioned external to the adsorbent region or even external the bed.Externally positioned sensors may detect the temperature of theadsorbent indirectly, such as through heat conducted from the adsorbent.

Controller 144 includes any suitable type and number of devices ormechanisms for comparing the measured temperature from at least onesensor 142 to at least one reference temperature and generating at leastan output signal responsive thereto if the measured temperature differsfrom the reference temperature by more than a preselected thresholdvalue. As illustrative, non-exclusive examples, controller 144 mayinclude one or more analog or digital circuits, logic units orprocessors for operating programs stored as software in memory, one ormore discrete units in communication with each other, etc. Controller144 may also regulate or control other portions of thehydrogen-generation assembly or fuel cell system and/or may be incommunication with other controllers adapted to control the operation ofthe hydrogen-generation assembly and/or fuel cell system. Controller 144is illustrated in FIG. 4 as being implemented as a discrete unit. It mayalso be implemented as separate components or controllers, such as acontroller for each bed. Such separate controllers, then, cancommunicate with each other and/or with other controllers present insystem 22 and/or assembly 46 via any suitable communication linkages.Further illustrative examples include a controller that receives thetemperature detected by one or more sensors 142, compares the one ormore measured temperatures with one or more reference temperatures, andgenerates, or selectively generates, an output signal responsivethereto. The output signal may be a command signal, such as to changethe operating state of the PSA assembly, hydrogen-generation assemblyand/or fuel cell system, and/or it may include a value or input that isreceived and processed by another controller to generate a desiredchange in operating state. In FIGS. 10-12, reference numeral 146schematically indicates that the controller is adapted to generate oneor more output signals responsive at least in part to the one or moremeasured temperatures and/or the relationship of this temperature to oneor more reference temperatures or threshold values. As discussed, thisrelationship may include comparing the temperatures and/or values todetermine if they deviate by more than a predetermined amount, if themeasured temperature is within a predetermined range of the referencetemperature or value, if the measured temperature is equal to, at leastas great as, and/or greater than the reference temperature, etc.

Illustrative, non-exclusive examples of suitable reference temperaturesinclude stored or previously measured temperatures or values. Otherexamples include another temperature measured by system 140, such as atemperature measured upstream (i.e., in the direction of the fuelprocessing system or other source of mixed gas stream 74 relative to thePSA assembly) or downstream (i.e., in the direction of fuel cell stack24 or other destination for product hydrogen stream 42 relative to thePSA assembly) from the measured temperature that is being compared tothe reference temperature. For example, system 140 may be adapted tocompare a measured temperature to previously measured temperatures fromthe sensor 142, to stored threshold values, and/or to one or moretemperatures measured by other sensors 142. The previously measuredand/or other threshold values may be stored in a memory portion of thecontroller. The memory portion may include volatile and/or non-volatileportions.

A benefit of a plurality of sensors spaced along the length of theadsorbent region is that the relative temperature within a particularregion may be determined. For example, because the temperature of theadsorbent in region 114 tends to increase in the mass transfer zone, itmay be desirable to compare the temperature of the adsorbent at or nearthe distal (relative to the mixed gas stream input port) end portion ofthe adsorbent region with the temperature of adsorbent upstream (i.e.,closer to the feed end of the adsorbent region through which the mixedgas stream is introduced into the adsorbent region) from this referencetemperature. As the mass transfer zone moves through the adsorbentregion, the relative increase and subsequent decrease in temperature ofadsorbent along the adsorbent region may provide an indicator of theposition of the mass transfer zone within the adsorbent region. This, inturn, provides an indicator of how close the bed is to being saturatedwith adsorbent, i.e., when the bed is nearing or at a breakthroughcondition. System 140 may be adapted to control the operation of atleast the PSA assembly responsive at least in part to whether or not abreakthrough condition is detected.

Another potential benefit of using a measured temperature as a referencetemperature is that the adsorbent bed, including adsorbent region 114thereof, will tend to increase or decrease in temperature during use ofthe PSA assembly, such as responsive to such factors as the flow rateand/or temperature of the mixed gas stream being delivered to the bed,the stage of the PSA process in which a bed is currently configured, theoperating conditions within the bed, the flow rate and/or temperature ofany purge gas stream being delivered to the bed, etc. While an absolutetemperature reading that is not correlated to any of these factors maybe used in some embodiments, it may be desirable to compare or otherwisecorrelate a detected temperature with at least one of a previouslydetected threshold temperature or range of temperatures, a stored orpreselected threshold temperature or range of temperatures, and/or oneor more temperatures measured elsewhere in the PSA assembly or the fluidstreams associated therewith, such as (but not limited to), upstream ordownstream in the same adsorbent region, elsewhere in the adsorbent bed,in the fluid streams delivered to or removed from the bed, etc.Therefore, by measuring the temperature of the adsorbent within theadsorbent region, system 140 may be adapted to calculate or otherwisedetermine the degree of saturation of the adsorbent within the adsorbentregion, the relative location of the mass transfer zone within theadsorbent region, when the mass transfer zone nears or reaches thedistal end or end portion of the adsorbent region, etc.

Upon detection of a breakthrough condition, and/or detection of ameasured temperature that exceeds a reference temperature or thresholdvalue, system 140, such as via controller 144, may be adapted todirectly or indirectly alter the operation of the PSA assemblyresponsive at least in part thereto to prevent actual breakthrough fromoccurring. Illustrative threshold values include predetermined thresholdtemperatures and temperature ranges corresponding to currently orpreviously measured temperatures or threshold temperatures, such as+/−1° C., 2° C., 3° C., 5° C., etc. Illustrative, non-exclusivesexamples of these responses include one or more of the following: atleast initially selecting, calculating, setting, or otherwisedetermining the cycle time of the PSA assembly and/or time periodsassociated with one or more steps of the PSA cycle, such as initiallyselecting, calculating, setting, or otherwise determining the durationof the adsorption step in the cycle; reducing, increasing, or otherwisechanging or varying the cycle time of the PSA assembly and/or timeperiods associated with one or more steps of the PSA cycle, such asreducing the adsorption time and/or increasing the purge time in thecycle starting, interrupting, stopping, and/or otherwise controlling oneor more steps of a PSA cycle, such as stopping the adsorption stepand/or starting the depressurization step (and optionally at least oneof the equalization step and the purge step); transitioning from onestep of a PSA cycle to another step of the PSA cycle, such astransitioning to the depressurization step or to the purge step of a PSAcycle; increasing or otherwise changing or varying the flow rate ofpurge gas during the purge step; starting, interrupting, stopping,and/or otherwise controlling the flow of the mixed gas stream throughone or more of the adsorbent beds and/or the PSA assembly, which mayinclude directing the mixed gas stream to transition from one adsorbentbed to another; shutting down the PSA assembly (and/or thehydrogen-generation assembly and/or the fuel cell system); otherwiseselecting, calculating, setting, or otherwise determining and/or varyingone or more operating parameters of the PSA assembly (such as a PSAcycle time, time periods associated with one or more steps of a PSAcycle, flow rates of mixed gas and/or purge streams, etc.); otherwiseautomatically adjusting the operation of the PSA assembly; alerting anoperator; and so forth.

While it is within the scope of the present disclosure, it is notrequired for all embodiments that system 140 shut down or otherwisealter the operating state of the PSA assembly (or hydrogen-generationassembly 46 or fuel cell system 22) immediately upon detecting abreakthrough condition. For example, the composition and/or flow rate ofmixed gas stream through the adsorbent region, including the portionthereof proximate a particular temperature sensor, may fluctuate duringuse of the PSA assembly. While these flows and compositions arepreferably relatively steady or constant, it should be appreciated thatvariations and fluctuations tend to occur. Accordingly, a detectedbreakthrough condition may cease to be detected shortly after initialdetection. Accordingly, in some embodiments, it may be desirable forsystem 140 to not stop or otherwise alter the operation of the PSAassembly (and/or assembly 46 and/or system 22) until a breakthroughcondition is detected and remains detected for more than a selected timeperiod (such as at least 1 second, 5 seconds, 10 seconds, 30 seconds,etc.) and/or is detected in two or more sequential PSA cycles.Relatedly, in some embodiments, it may be desirable for the measuredtemperature to be measured upstream from the distal end of the adsorbentregion to provide a region of adsorbent between the adsorbent whosetemperature is detected and the distal end of the adsorbent region. Forexample, detecting the measured temperature associated with theadsorbent within the distal third (or less of the adsorbent region) butnot within the final 20%, 10%, 5% or 3% of the adsorbent region mayprovide a period of time to confirm the presence of a breakthroughcondition and implement a desired change in the operating state of thePSA assembly (and/or assembly 46 and/or system 22). Accordingly, theterm “detection of a breakthrough condition,” as used herein, may referto an initial detection of a breakthrough condition, and/or mayoptionally refer to subsequent continuous or discontinuous detection ofa breakthrough condition following an initial detection.

Upon detection of a breakthrough condition, system 140 may be adapted toshut down the PSA assembly (and/or an associated hydrogen-generationassembly 46 and/or fuel cell system 22). This shutdown may beimplemented via any suitable sequence of steps, such as ranging from animmediate shutdown of the assembly and all associated systems, to acontrolled shutdown in which the assembly (and associated devices)follow a prescribed sequence of shutdown steps. For example, theshutdown step may include equalizing the bed to harvest the hydrogen gascontained therein and to utilize at least some of the pressure withinthe bed. As another example, the shutdown steps may include cycling thePSA assembly through one or more, such as 2-20, 3-10, 4-8, 6, etc.shorter PSA cycles. A potential benefit of shutting down the PSAassembly with a series of shorter PSA cycles is that the adsorbent bedmay be regenerated and thereby ready for use when the system is startedup again. A variation of shorter overall PSA cycles is a longer purgestep and/or greater purge volume of gas relative to the purge andadsorption steps utilized in the PSA cycles prior to beginning theshutdown routine.

Another suitable response by system 140 to the detection of abreakthrough condition is to select, calculate, set, or otherwisedetermine, at least initially, a suitable time period for one or moresteps of the PSA cycle, and/or the overall cycle time of the PSAassembly. As an illustrative and non-limiting example, upon systemstartup, and/or delivery of the mixed gas stream to the PSA assembly, aninitial time period for at least the adsorption step may be selected,calculated, set, or otherwise determined by allowing the mixed gasstream to flow to an adsorbent region in an adsorbent bed until abreakthrough condition is detected, until a threshold temperature ismeasured, and/or until a threshold value is reached. In other words, inthis example, the adsorption step proceeds until the breakthroughcondition is detected, instead of the cycle time being predeterminedunless prematurely interrupted or stopped by the detection of abreakthrough condition. Any of the detection mechanisms and referencetemperatures described herein may be utilized.

Optionally, an initial or current time period, or set of time periods,for one or more steps of a PSA cycle, and/or an initial or current PSAcycle time (such as initially determined, as predetermined, or asotherwise determined prior to initiation of the current step or PSAcycle) may be changed or otherwise varied in subsequent PSA cycles, suchas responsive to the temperature-based breakthrough detection system orotherwise to the relationship between the measured temperature and areference temperature. For example, the duration of an adsorption stepmay be reduced, and/or the length of a purge step may be increased,relative to the time periods associated with such steps in previous PSAcycles, based at least in part on the relationship between the measuredtemperature and a reference temperature.

Accordingly, a further illustrative, non-exclusive example of a suitableresponse by system 140 to the detection of a breakthrough condition isto continue to operate the PSA assembly but with a shorter cycle timeand/or a longer purge time and/or greater flow rate of purge gas, ascompared to these relative values, such as initial values or otherwise,as utilized in the PSA cycle prior to the detection of the breakthroughcondition. For example, upon detection of a breakthrough condition,system 140 may be adapted to shorten at least one of the overall cycletime or the adsorption time by a predetermined increment, such as 5%,10%, 15%, or more. The PSA assembly may then continue to be operatedwith this new cycle time. If the breakthrough condition continues to bedetected, the cycle time may again be decreased by the same or adifferent predetermined increment, or otherwise varied. System 140 may(but is not required to) shut down the PSA assembly if the cycle time oradsorption time reach or exceed preselected minimum cycle times oradsorption times. As used herein, shortening of a duration or timeperiod may be a reduction but not elimination of this time period. Forexample, reducing the cycle time is not intended to mean automaticallyshutting down the PSA assembly, and reducing the cycle time by anincrement is not intended to mean an increment of 100% of the currentcycle time (i.e., shutting down operation of the PSA assembly). Shuttingdown of the PSA assembly and/or stopping of a PSA cycle or step of a PSAcycle are still responses that are within the scope of the presentdisclosure, but they are described differently than simply a reductionin the corresponding time period.

Similar to the above-discussed variants of illustrative shutdownroutines, a variant of the above response (i.e., shortening the cycletime and/or the adsorption time) is to lengthen the purge time and/orincrease the flow rate of purge gas. Preferably, the decrease inadsorption or cycle time and/or the increase in purge time and/or purgeflow should urge the mass transfer zone toward the feed end of theadsorption region. As a further variant, system 140 may be adapted tofollow the decrease in cycle or adsorption time with an increase in thistime (and/or decrease in the purge time/flow) by a second predeterminedincrement. This second increment may be the same as, shorter than, orlonger than the increment by which the time was previously decreased. Asdiscussed, the shorter cycle time or other corrective steps may besufficient to partially regenerate the adsorbent, and thereby move themass transfer zone away from the distal end of the adsorbent region.Therefore, the cycle time may be returned to or toward its originalstate. Should the breakthrough condition be subsequently detected again,the time may again be decreased by a predetermined increment, etc.System 140 may be adapted to wait until the breakthrough condition isnot detected in any of the beds and/or not detected for a selectednumber of cycles, such as 2 cycles, 3 cycles, 5-10 cycles, etc., beforeincreasing the cycle time or otherwise returning the operatingconditions to or toward the original conditions.

Other illustrative, non-exclusive examples of suitable responses bysystem 140 to the detection of a breakthrough condition are to cause,such as through suitable input or command signals, the PSA assembly tostop, start, interrupt, increase in duration, decrease in duration,and/or otherwise control one or more steps of a PSA cycle. For example,system 140 may stop the adsorption step of the bed in which thebreakthrough condition is detected. Such responses may optionallyinclude, or otherwise be accompanied by, transitioning from one step ofthe PSA cycle to another of the steps of the PSA cycle responsive to therelationship between the measured temperature and a referencetemperature. For example, the PSA assembly may be directed, by system140, to transition to the depressurization step, such as when theadsorption step is stopped.

Another illustrative, non-exclusive example of a suitable response bysystem 140 to the detection of a breakthrough condition includescontrolling the mixed gas stream, such as increasing, decreasing, orotherwise varying the flow rate of the mixed gas stream, directing themixed gas stream, and so forth. For example, when a breakthroughcondition is detected, the controller may direct, such as via one ormore output or command signals, the flow of the mixed gas stream to bestopped to the bed in which the breakthrough condition was detected,with the flow of mixed gas stream being directed to another bed in thePSA assembly for purifying the mixed gas stream. As discussed, this mayinclude stopping the flow of mixed gas stream to the bed in which thebreakthrough condition was detected and/or the flow of product hydrogenstream from the bed, equalizing the bed, depressurizing and purging thebed, etc. The bed in which the breakthrough condition was detected mayproceed through its equalization, depressurization, and/or purge steps,as discussed.

Another illustrative, non-exclusive example of a response to thedetection of a breakthrough condition by system 140 is an alert, such asto an operator or other user. The alert may be provided via any suitablemechanism and may be generated proximate the PSA assembly and/or remotefrom the assembly. For example, the alert may be implemented withaudible and/or visual signals, electronic signals, electronic notices,and the like. When system 140 is adapted to generate an alert responsiveto the detection of a breakthrough condition, it may be further adaptedto generate one or more of a plurality of alerts, such as depending uponsuch factors as the elapsed time since the breakthrough condition wasdetected, the number of PSA cycles elapsed since the breakthroughcondition was detected, the portion of the adsorbent region in which thebreakthrough condition was detected, the proximity of the adsorbent inwhich the breakthrough condition was detected with the distal end of theadsorbent region, etc. For example, a first alert may be generated uponinitial detection of a breakthrough condition, with further (optionallydistinguishable) alerts being generated as the breakthrough conditioncontinues to be detected and/or as the location of the condition movestoward the distal end of the adsorbent region.

It is within the scope of the present disclosure that PSA assemblies 73with temperature-based breakthrough detection systems 140 according tothe present disclosure may implement more than one of the illustrativeresponses to the detection of a breakthrough condition described hereinand/or may be adapted to detect any of the illustrative breakthroughconditions, or triggering events, described herein.

It is also within the scope of the present disclosure that the steps ofthe PSA cycle may have any suitable length, i.e. represent any suitableportion of the total cycle time of the PSA assembly. As mentioned above,one or more of these steps may include a time that is previouslyselected, such as a fixed equalization time. Similarly, one or more ofthese times may be a percentage of the adsorption time. Typically, thetime for these steps will be within 50-150% of the time for theseparation system. As an illustrative example, equal times may be used,but it is within the scope of the present disclosure that times outsideof this range may be used.

Illustrative, non-exclusive examples of implementations oftemperature-based breakthrough detection systems 140 include, but arenot limited to, one or more of the following implementations, which maybe implemented in one or more of a PSA assembly, a PSA assembly adaptedto purify hydrogen gas, a hydrogen-generation assembly including a fuelprocessor adapted to produce a mixed gas stream containing hydrogen gasas its majority component and other gases and a PSA assembly adapted toproduce a product hydrogen stream from the mixed gas stream, a PSAassembly adapted to remove impurities from a hydrogen-rich stream for afuel cell stack, a fuel cell system containing a fuel cell stack, ahydrogen-purifying PSA assembly and a source of hydrogen gas to bepurified by the PSA assembly (with the source optionally including afuel processor, and in some embodiments a steam reformer), and ahydrogen-generation assembly including a fuel processor adapted toproduce a mixed gas stream containing hydrogen gas as its majoritycomponent and other gases and a PSA assembly adapted to removeimpurities (including carbon monoxide) from the mixed gas stream (andoptionally a fuel cell stack adapted to receive at least a portion ofthe purified mixed gas stream):

A temperature-based detection system adapted to determine the cycle timefor a PSA assembly responsive at least in part to a measured temperaturewithin the adsorbent region of the assembly.

A temperature-based detection system adapted to determine the cycle timefor a PSA assembly responsive at least in part to the relationshipbetween a measured temperature within the adsorbent region of theassembly and a reference temperature.

A temperature-based detection system adapted to determine the cycle timefor a PSA assembly responsive at least in part to the relationshipbetween a measured temperature within the adsorbent region and areference temperature that is also associated with one or more ofanother portion of the adsorbent region, the gas flowing into, throughor out of an adsorbent bed, and components of the adsorbent bed.

A temperature-based detection system adapted to detect impendingbreakthrough of carbon monoxide in an adsorbent region of a PSA assemblywithout measuring the concentration of carbon monoxide in or associatedwith the adsorbent region, and optionally without measuring theconcentration of any gases in or associated with the adsorbent region.

A temperature-based detection system adapted to set, regulate,calculate, or otherwise determine a time period associated with one ormore steps of the PSA cycle in a PSA assembly responsive at least inpart to a measured temperature within the adsorbent region of theassembly.

A temperature-based detection system adapted to set, regulate,calculate, or otherwise determine a time period associated with one ormore steps of the PSA cycle in a PSA assembly responsive at least inpart to the relationship between a measured temperature within theadsorbent region of the assembly and a reference temperature.

A temperature-based detection system adapted to set, regulate,calculate, or otherwise determine or establish the adsorption time for aPSA cycle based upon one or more temperatures measured within anadsorbent bed of the PSA assembly, and optionally upon one or moretemperatures measured in an adsorbent region thereof.

A temperature-based detection system adapted to transition from at leastone of the steps of a PSA cycle to another of the steps of a PSA cycleresponsive at least in part to the relationship between a measuredtemperature within the adsorbent region of the assembly and a referencetemperature.

A temperature-based detection system adapted to prevent breakthrough inan adsorbent bed of a PSA assembly by monitoring at least one measuredtemperature associated with the adsorbent bed, and optionally, theadsorbent in the adsorbent bed, and comparing the at least one measuredtemperature to at least one reference temperature.

A temperature-based detection system adapted to set, regulate,calculate, or otherwise determine the position of the, or the primary,mass transfer zone within an adsorbent region of an adsorbent bed of aPSA assembly.

A temperature-based detection system adapted to decrease, such as by apercentage that is less than 100%, the PSA cycle time in a PSA assemblyresponsive at least in part to one or more measured temperaturesassociated with the adsorbent in an adsorbent region of the PSAassembly.

A temperature-based detection system adapted to shut down a PSAassembly, a hydrogen-generation assembly adapted to produce ahydrogen-containing mixed gas stream to be purified into a producthydrogen stream by the PSA assembly, and/or a fuel cell stack adapted toreceive at least a portion of the product hydrogen stream responsive atleast in part to one or more measured temperatures associated with theadsorbent in an adsorbent region of the PSA assembly.

A temperature-based detection system adapted to stop the adsorption stepof a PSA cycle responsive at least in part to one or more measuredtemperatures associated with the adsorbent in an adsorbent region of thePSA assembly.

A temperature-based detection system adapted to stop the flow of themixed gas stream to the adsorbent region of a first adsorbent bed in thePSA assembly and/or direct the flow of the mixed gas stream to theadsorbent region of a second adsorbent bed in the PSA assemblyresponsive at least in part to the relationship between a measuredtemperature within the adsorbent region of the first bed and a referencetemperature.

A temperature-based detection system adapted to generate at least onealert or other notification responsive at least in part to one or moremeasured temperatures associated with the adsorbent in an adsorbentregion of the PSA assembly.

A temperature-based detection system adapted to control the operationand/or change the operating state of a fuel processing system adapted toproduce a mixed gas stream to be purified by a PSA assembly responsiveat least in part to one or more measured temperatures associated withthe adsorbent in an adsorbent region of the PSA assembly.

A temperature-based detection system adapted to control the operationand/or change the operating state of a fuel cell system containing a PSAassembly responsive at least in part to one or more measuredtemperatures associated with the adsorbent in an adsorbent region of thePSA assembly.

A temperature-based detection system adapted to detect a breakthroughcondition in a PSA assembly, including in an adsorbent bed thereofand/or in an adsorbent region of an adsorbent bed thereof.

A temperature-based detection system adapted to detect a breakthroughcondition in a PSA assembly, including in an adsorbent bed thereofand/or in an adsorbent region of an adsorbent bed thereof, andresponsive at least in part thereto to adjust or otherwise control theoperation of at least the PSA assembly, and optionally an associatedfuel processing system, fuel cell stack, hydrogen-generation assemblyand/or fuel cell system.

A temperature-based detection system adapted to selectively increaseand/or decrease one or more of the time periods associated with one ormore steps of a PSA cycle, the overall PSA cycle time, the purge timeand/or the fuel gas flow rate responsive to one or more measuredtemperatures associated with adsorbent in an adsorbent region of the PSAassembly.

Any of the above detection systems in which the system is adapted tocompare one or more measured temperatures with one or more referencetemperatures, with the reference temperatures selectively including oneor more measured temperatures, one or more stored values, one or morepreviously measured temperatures and/or one or more threshold values.

Any of the above detection systems in which the system is adapted todetermine if a measured temperature is within a predetermine range(above and/or below) of one or more reference temperatures, equals oneor more reference temperatures, and/or exceeds one or more referencetemperatures.

Any of the above detection systems in which the system is adapted tocompare one or more measured temperatures with one or more referencetemperatures, with the reference temperatures selectively including oneor more measured temperatures, one or more stored values, one or morepreviously measured temperatures and/or one or more threshold values.

Any of the above detection systems, and implementations thereof,expressed as a temperature-based breakthrough prevention system.

Any of the above detection systems implemented with a PSA assemblyhaving a plurality of adsorbent beds adapted to receive a mixed gasstream that includes hydrogen gas as its majority component and which isproduced by a fuel processing system that includes at least onereforming region adapted to produce the mixed gas stream by steamreforming water and a carbon-containing feedstock, with at least thereforming region(s) of the fuel processing system adapted to be heatedby a heating assembly, optionally with the PSA assembly adapted toprovide at least one fuel stream to the heating assembly, and optionallyin further combination with a fuel cell stack adapted to receive atleast a portion of the purified hydrogen gas produced by the PSAassembly.

Methods for implementing the processes of any of the above systemsand/or use of any of the above systems.

Although discussed herein in the context of a PSA assembly for purifyinghydrogen gas, it is within the scope of the present disclosure that thePSA assembly and/or temperature-based breakthrough detection systemdisclosed herein may be used in other applications, such as to purifyother mixed gas streams in fuel cell or other systems.

INDUSTRIAL APPLICABILITY

The pressure swing adsorption assemblies and hydrogen-generation and/orfuel cell systems including the same are applicable in the gasgeneration and fuel cell fields, including such fields in which hydrogengas is generated, purified and/or consumed to produce an electriccurrent.

It is believed that the disclosure set forth above encompasses multipledistinct inventions with independent utility. While each of theseinventions has been disclosed in its preferred form, the specificembodiments thereof as disclosed and illustrated herein are not to beconsidered in a limiting sense as numerous variations are possible. Thesubject matter of the inventions includes all novel and non-obviouscombinations and subcombinations of the various elements, features,functions and/or properties disclosed herein. Similarly, where theclaims recite “a” or “a first” element or the equivalent thereof, suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.

It is believed that the following claims particularly point out certaincombinations and subcombinations that are directed to one of thedisclosed inventions and are novel and non-obvious. Inventions embodiedin other combinations and subcombinations of features, functions,elements and/or properties may be claimed through amendment of thepresent claims or presentation of new claims in this or a relatedapplication. Such amended or new claims, whether they are directed to adifferent invention or directed to the same invention, whetherdifferent, broader, narrower, or equal in scope to the original claims,are also regarded as included within the subject matter of theinventions of the present disclosure.

1. A hydrogen-generation assembly, comprising: a hydrogen-producingassembly adapted to produce a mixed gas stream containing hydrogen gasand other gases from at least one feedstock; a pressure swing adsorptionassembly adapted to receive at least a portion of the mixed gas streamand to reduce the concentration of the other gases therefrom through aPSA cycle that includes at least pressurization, adsorption,depressurization, and purge steps and which has a cycle time to producea product hydrogen stream having greater hydrogen purity than the mixedgas stream; the pressure swing adsorption assembly comprising: aplurality of adsorbent beds, each bed including an adsorbent regioncontaining adsorbent adapted to adsorb at least one of the other gases;and a temperature-based detection system, comprising: at least onetemperature sensor adapted to measure a temperature associated with aportion of the adsorbent region; and a controller adapted to compare thetemperature associated with a portion of the adsorbent region with atleast one reference temperature that includes a temperature associatedwith a second portion of the adsorbent region and to selectively controlthe operation of at least the pressure swing adsorption assemblyresponsive at least in part thereto, wherein the temperature-baseddetection system is adapted to transition from at least one of thepressurization, adsorption, depressurization, and purge steps of the PSAcycle to another of the steps of the PSA cycle responsive to therelationship between the measured temperature and the referencetemperature.
 2. The assembly of claim 1, wherein the temperature-baseddetection system is adapted to transition to at least one of thedepressurization and the purge steps of the PSA cycle responsive to therelationship between the measured temperature and a referencetemperature.
 3. The assembly of claim 1, wherein the temperature-baseddetection system is adapted to initially determine the cycle time of thePSA cycle responsive to the relationship between the measuredtemperature and a reference temperature.
 4. The assembly of claim 1,wherein the temperature-based detection system is adapted to vary thecycle time of the PSA cycle responsive to the relationship between themeasured temperature and a reference temperature.
 5. The assembly ofclaim 4, wherein the cycle time of the PSA cycle is reduced responsiveto the relationship between the measured temperature and a referencetemperature.
 6. The assembly of claim 4, wherein the temperature-baseddetection system is adapted to vary the cycle time by a predeterminedincrement responsive to the relationship between the measuredtemperature and a reference temperature.
 7. The assembly of claim 1,wherein the cycle time includes a time period associated with each ofthe steps in the PSA cycle, and further wherein the temperature-baseddetection system is adapted to initially determine the time periodassociated with at least one step of the PSA cycle responsive to therelationship between the measured temperature and a referencetemperature.
 8. The assembly of claim 1, wherein the cycle time includesa time period associated with each of the steps in the PSA cycle, andfurther wherein the temperature-based detection system is adapted tochange the time period associated with at least one step of the PSAcycle responsive to the relationship between the measured temperatureand a reference temperature.
 9. The assembly of claim 8, wherein thetemperature-based detection system is adapted to reduce the time periodassociated with the adsorption step of the PSA cycle responsive to therelationship between the measured temperature and a referencetemperature.
 10. The assembly of claim 8, wherein the temperature-baseddetection system is adapted to increase the time period associated withthe purge step of the PSA cycle responsive to the relationship betweenthe measured temperature and a reference temperature.
 11. The assemblyof claim 8, wherein the temperature-based detection system is adapted tochange the time period associated with the purge step of the PSA cycleby a predetermined increment responsive to the relationship between themeasured temperature and a reference temperature.
 12. The assembly ofclaim 1, wherein the temperature-based detection system is furtheradapted to control the operation of the pressure swing adsorptionassembly responsive at least in part to the relationship of the measuredtemperature to a reference temperature.
 13. The assembly of claim 12,wherein control of the operation of the pressure swing adsorptionassembly further comprises directing the flow of the mixed gas stream toan adsorbent bed of the pressure swing adsorption assembly, and whereinthe temperature-based detection system is adapted to stop the flow ofthe mixed gas stream to the adsorbent bed responsive at least in part tothe relationship of the measured temperature and a referencetemperature.
 14. The assembly of claim 13, wherein control of theoperation of the pressure swing adsorption assembly further comprisesdirecting the flow of the mixed gas stream to an adsorbent bed of thepressure swing adsorption assembly, and wherein the temperature-baseddetection system is adapted to stop the flow of the mixed gas stream tothe adsorbent bed responsive at least in part to the relationship of themeasured temperature and a reference temperature.
 15. The assembly ofclaim 13, wherein the temperature-based detection system is furtheradapted, subsequent to stopping the flow of the mixed gas stream to theadsorbent bed responsive at least in part to the relationship of themeasured temperature and a reference temperature, to start thedepressurization step of the PSA cycle of the adsorbent bed.
 16. Amethod for preventing breakthrough in a pressure swing adsorptionassembly with at least one adsorbent bed having an adsorbent regioncontaining at least one adsorbent adapted to adsorb impurities in animpure hydrogen stream to produce a purified hydrogen stream therefrom,the method comprising: detecting a measured temperature associated witha portion of the adsorbent region; detecting a reference temperatureassociated with a second portion of the adsorbent region downstream fromthe portion of the adsorbent region from which the measured temperatureis detected; comparing the measured temperature and the referencetemperature; and automatically adjusting the operation of the pressureswing adsorption assembly responsive to the measured temperatureexceeding the reference temperature by more than a threshold value,wherein the automatically adjusting includes automatically adjusting atleast one operating parameter of the pressure swing adsorption assembly,wherein automatically adjusting the operation of the pressure swingadsorption assembly includes controlling the flow of the impure hydrogenstream through the adsorbent region in which the measured temperature isdetected.
 17. The method of claim 16, wherein the at least one operatingparameter includes a time period in which the impure hydrogen streamflows through the adsorbent region in which the measured temperature isdetected.
 18. The method of claim 16, wherein the pressure swingadsorption assembly is adapted to reduce the concentration of the othergases in the impure hydrogen stream through a PSA cycle that includes atleast pressurization, adsorption, depressurization, and purge steps andwhich has a cycle time, and wherein the at least one operating parameterincludes a time period associated with at least one of the steps in thePSA cycle.
 19. The method of claim 18, wherein the automaticallyadjusting includes one or more of increasing or reducing the time periodassociated with the purge step of the PSA cycle.
 20. The method of claim18, wherein the automatically adjusting includes one or more ofincreasing or reducing the time period associated with the adsorptionstep of the PSA cycle.
 21. The method of claim 16, wherein the pressureswing adsorption assembly is adapted to reduce the concentration of theother gases in the impure hydrogen stream through a PSA cycle thatincludes at least pressurization, adsorption, depressurization, andpurge steps and which has a cycle time, and wherein the automaticallyadjusting includes transitioning from at least one of the steps of thePSA cycle to another of the steps of the PSA cycle responsive to therelationship between the measured temperature and a referencetemperature.
 22. A hydrogen-generation assembly, comprising: a source ofa mixed gas stream containing hydrogen gas and other gases from at leastone feedstock; a pressure swing adsorption assembly adapted to receiveat least a portion of the mixed gas stream and to reduce theconcentration of the other gases therefrom through a PSA cycle thatincludes at least pressurization, adsorption, depressurization, andpurge steps and which has a cycle time to produce a product hydrogenstream having greater hydrogen purity than the mixed gas stream; thepressure swing adsorption assembly comprising: a plurality of adsorbentbeds, each bed including an adsorbent region containing adsorbentadapted to adsorb at least one of the other gases; and means forcontrolling the duration of at least one step of the PSA cycleresponsive to comparison of a temperature associated with a portion ofthe adsorbent region and at least one reference temperature.
 23. Thehydrogen-generation assembly of claim 22, wherein the at least onereference temperature is not associated with the portion of theadsorbent region to which the temperature is associated.
 24. Thehydrogen-generation assembly of claim 22, wherein the temperature andthe reference temperature are respectively associated with differentportions of the adsorbent region.